Orientation Sensing With a Loop Resonator Based on Its Re-Radiation Pattern

This article presents an analytical model of the radiation pattern of a loop resonator, which is frequently used as chipless radio-frequency iDentification (RFID) tags. The radiation pattern of this resonator can be used in practice as a sensor to determine the orientation between the tag and the antenna. Contrary to already implemented chipless RFID angle sensors, the one introduced here allows to extract rotation of the tag or the antenna position in 3-D using a novel approach based on the resonator radiation pattern. An analytical model is developed to measure the tag orientation determining both the inclination and azimuthal angle of the tag in a spherical coordinates system for both monostatic and bistatic antenna configurations. Uncertainties are studied with Monte Carlo simulations. Simulations and measurements are performed to validate the orientation extraction and evaluate the performance of the proposed solution. We show that the accuracy of this totally passive and wireless sensor is always below 5 degrees in the measurable range with a maximum error lower than 3 degrees for the monostatic case.